Sites for launching large rockets are often equipped with asound suppression system to absorb or deflectacoustic energy generated during a rocket launch. As engine exhaust gasses exceed thespeed of sound, they collide with the ambient air andshockwaves are created, with noise levels approaching 200 db. This energy can be reflected by thelaunch platform and pad surfaces, and could potentially cause damage to the launch vehicle, payload, and crew. For instance, the maximum admissible overallsound power level (OASPL) for payload integrity is approximately 145 db.[1] Sound is dissipated by huge volumes of water distributed across the launch pad and launch platform during liftoff.[2][3]
Water-based acoustic suppression systems are common on launch pads. They aid in reducing acoustic energy by injecting large quantities of water below the launch pad into the exhaust plume and in the area above the pad.Flame deflectors or flame trenches are designed to channel rocket exhaust away from the launch pad but also redirect acoustic energy away.[2][4]
The launch pad built by the Soviet Union beginning in 1978 at theBaikonur Cosmodrome for launching theEnergiya rocket included an elaborate sound suppression system which delivered a peak flow of 18 cubic metres (4,800 US gal) per second fed by three ground level reservoirs totaling 18,000 cubic metres (4,800,000 US gal).[5]
Data from the launch ofSTS-1 found an overpressure wave created by the shuttle's three SSME (now designated RS-25) liquid-fueled rocket engines and the four-segment solid rocket boosters contributed to the loss of sixteen and damage to an additional 148thermal protection tiles prompting modifications to theSound Suppression Water System (SSWS) installed at both launch pads atKennedy Space Center's Launch Complex 39.[6][7]
The resulting gravity fed system, used through the remainder of the program, began release from a 300,000-US-gallon (1.1-million-litre)water tower at the launch site 6.6 seconds before main engine start through 7 feet (2.1 m) diameter pipes connected to themobile launch platform. Water flowed out six 12-foot-high (3.7 m) towers known as "rainbirds" onto the launch platform and flame trench below, emptying the system in 41 seconds[8] with a peak flow of reducing acoustic energy levels to approximately 142dB.[9]
The massive white clouds that billowed around the shuttle at each launch were not smoke, butwet steam generated as the rocket exhaust boiled away huge quantities of water.[10]
Launch pad 0 at the Mid-Atlantic Spaceport atNASA's Wallops Flight Facility in Virginia is equipped with a 950,000 litres (250,000 US gal) water tower 307 feet (94 m) above the ground, among the tallest in the world. Engine exhaust exits through ring of water jets in the launch platform, directly beneath engine nozzles. The system is capable of delivering 4,000 US gallons (15 m3) per second.[11][12] Additional storage tanks totaling 100,000 US gallons (380,000 L; 83,000 imp gal) may be added forstatic fire tests. Water not vaporized is held in a 1,200 square metres (13,000 sq ft)retention basin where it is tested before release.[13]
Following the retirement of theSpace Shuttle program, pad B at launch complex 39 was upgraded for launches of theSpace Launch System (SLS). SLS features an additionalRS-25 liquid-fueledrocket engine along with an additional segment in each of its solid rocket boosters over the Space Shuttle program prompting upgrades to the system creating theIgnition Over-Pressure/Sound Suppression Water System (IOP/SS).
The control system was upgraded including replacement of nearly 250 miles (400 km) of copper cables with 57 miles (92 km) of fiber optic cable. Capacity was upgraded to 400,000 US gallons (1,500,000 L) with a peak flow rate of 1,100,000 US gallons (4,200,000 L) per minute. The upgraded system was tested in December 2018 with 450,000 US gallons (1,700,000 L).[14]
JAXA "seeks to achieve the world's quietest launch" from theirNoshiro Rocket Testing Center inAkita with the installation of a sound suppression water system as well as sound absorbing walls. The H3 Scaled Acoustic Reduction Experiment completed in 2017 provided additional data about the noise generated during liftoff.[15][16]